Google Has 10,000 Human Evaluators?

In the Seattle Conference on Scalability, Google's Marissa Mayer was asked a question where she revealed that Google has 10,000 human evaluators that manually go through the search results and rate them.

A: They have a bunch of watchdog services that track uptime for various servers to make sure a bad one isn't causing problems. In addition, they have 10,000 human evaluators who are always manually checking the relevance of various results.